The present invention relates to a method for moving a machine element of an automation machine and to a drive system.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Machine tools, in particular, are often provided with so-called redundant kinematics. In this case, redundant kinematics are understood as meaning the possibility of moving a machine element, which may be in the form of a tool receiving apparatus or a tool which is clamped in the tool receiving apparatus for example, along a direction with the aid of two separate drive shafts.
FIG. 1 uses a schematically illustrated machine tool 36 to illustrate the principle of redundant kinematics. A carrier 5 can be moved in a direction X with the aid of two linear motors 3 and 4. The guidance of the movement in the X direction is ensured by two columns 1 and 2 in this case. A further column 6 which is used to guide the movement of a second linear motor 7 is fastened to the carrier 5. The linear motor 7 likewise moves in the X direction. The direction of movement of the linear motors 3, 4 and 7 is indicated by depicted arrows 37, 12 and 13. A machine element 8 which is in the form of a tool receiving apparatus within the scope of the exemplary embodiment is fitted to the linear motor 7. A tool 9 is clamped in the tool receiving apparatus.
It goes without saying that the machine tool 36 also has further motors which allow a movement of the machine element 8, for example in the Y and Z directions, but are not illustrated in FIG. 1 for the sake of clarity and since they are irrelevant to understanding the invention.
In order to measure a first actual variable xc,ist which indicates the position of the column 6 with respect to a stationary machine bed 35 of the machine, the machine 36 has a first measuring device which is not illustrated in FIG. 1 for the sake of clarity. In order to measure a second actual variable xf,ist which indicates the position of the machine element 8 with respect to the column 6, the machine tool 36 has a second measuring device which is likewise not illustrated in FIG. 1 for the sake of clarity.
If the machine element 8 is intended to be moved to a particular desired position value in the direction X, the problem arises of how the movement required for this purpose is intended to be divided between the two linear motors 3 and 4 and the linear motor 7. Since the linear motor 7 must move only small masses (machine element 8 and tool 9), it is able to carry out dynamic movements (for example movements with high accelerations) in the X direction, whereas the two linear motors 3 and 4 can carry out only relatively sluggish movements on account of the larger masses to be moved by them. It is therefore expedient to divide the movement of the machine element into a first movement component, which is carried out by the two linear motors 3 and 4, and a second movement component which is carried out by the linear motor 7. In this case, the first movement component comprises the movement processes which are not very dynamic, that is to say the low-frequency movement processes, whereas the second movement component comprises the dynamic, that is to say high-frequency, movement processes of the machine element.
FIG. 2 illustrates a schematic block illustration of a drive system which is known to be commercially available for the machine tool 36. A desired variable generating unit 15 which is generally part of a control device 14, which may be in the form of a CNC controller for example, generates a first desired variable xsoll which is in the form of a desired position variable within the scope of the exemplary embodiment according to FIG. 1 and indicates the desired position of the machine element 8 with respect to the machine bed 35. The first desired variable xsoll is supplied, as a controlled desired variable for regulating the first movement component of the machine element 8, to a first regulating means 16a. The first actual variable xc,ist which is measured using a first measuring device 10 and indicates the position of the column 6 with respect to the machine bed 35 within the scope of the exemplary embodiment according to FIG. 1 is also supplied to the first regulating unit 16a as a controlled actual variable. The first actual variable xc,ist indicates the first movement component of the machine element 8 by indicating the position of the column 6 with respect to the machine bed 35 within the scope of the exemplary embodiment according to FIG. 1.
The first regulating means 16a drives a first power converter 17a, which is illustrated by an arrow 18a in FIG. 2, in accordance with the first desired variable xsoll and the first actual variable xc,ist. The first desired variable xsoll is the controlled desired variable for regulating the first movement component of the machine element 8. The first power converter 17a accordingly drives the two linear motors 3 and 4, which is illustrated by an arrow 19a, the linear motors 3 and 4 moving a load 19. In this case, the load 19 comprises all elements which are moved by the linear motors 3 and 4 in the direction X. The first regulating means 16a, the first power converter 17a, the linear motors 3 and 4, the load 19 and the measuring device 10 form a first drive shaft 20a which is used to carry out the first movement component of the machine element 8.
In order to regulate the second movement component of the machine element 8, the so-called contouring error s is determined in the prior art by subtracting the first actual variable xc,ist from the first desired variable xsoll using a subtractor 22. The contouring error s is supplied, as a controlled desired variable for regulating the second movement component of the machine element 8, to a second regulating means 16b. The second actual variable xf,ist which is measured using a second measuring device 11 and indicates the position of the machine element 8 with respect to the column 6 within the scope of the exemplary embodiment according to FIG. 1 is also supplied to the second regulating unit 16b as a controlled actual variable. The second actual variable xf,ist indicates the second movement component of the machine element 8 by indicating the position of the machine element 8 with respect to the column 6 within the scope of the exemplary embodiment according to FIG. 1.
The second regulating means 16b drives a second power converter 17b, which is illustrated by an arrow 18b in FIG. 2, in accordance with the contouring error s and the second actual variable xf,ist. The second power converter 17b accordingly drives the linear motor 7, which is illustrated by an arrow 19b, the linear motor 7 moving a load 21. In this case, the load 21 comprises all elements which are moved by the linear motor 7 in the direction X. The second regulating means 16b, the second power converter 17b, the linear motor 7, the load 21 and the measuring device 11 form a second drive shaft 20b which is used to carry out the second movement component of the machine element 8.
It is noted at this point that the desired variable generating unit 15 likewise generates corresponding desired values for controlling the movement of the drive shafts which are used to move the machine element in the Y and Z directions. These desired values and the drive shafts which are used to move the machine element in the Y and Z directions are not illustrated in FIG. 2 and the subsequent figures for the sake of clarity and since they are irrelevant to understanding the invention.
FIG. 3 again illustrates the drive system shown in FIG. 2 in a simplified manner in the form of a block function diagram. In this case, the same elements are provided with the same reference symbols as in FIG. 2. In this case, the first drive shaft 20a has a transfer function G(s) and the second drive shaft 20b has a transfer function F(s). The overall position xist of the machine element 8, that is to say its position with respect to the machine bed 35 (see FIG. 1), results from adding the first actual variable xc,ist and the second actual variable xf,ist.
FIG. 4 illustrates another drive system which is known from the prior art, in which a movement is divided into a first movement component and a second movement component. The embodiment according to FIG. 4 is identical to the embodiment according to FIG. 2 insofar as it relates to the first drive shaft 20a and the second drive shaft 20b. In FIG. 4, the same elements are therefore provided with the same reference symbols as in FIG. 2. The fundamental difference in the embodiment according to FIG. 4 is that the control device 14′ has been extended by a dividing unit 23 in comparison with the control device 14 according to FIG. 2. The desired variable generating unit 15 generates a desired variable x′soll, which corresponds to the first desired variable xsoll according to FIG. 2. The dividing unit 23 uses the desired variable x′soll to determine a first desired variable xc,soll, which is supplied to the regulating means 16a as a controlled desired variable, and a second desired variable xf,soll which is supplied to the regulating means 16b as a controlled desired variable.
FIG. 5 again illustrates the control device 14′ and, in particular, the dividing unit 23 in detail, the same elements in FIG. 5 being provided with the same reference symbols as in FIG. 4. In order to divide the movement, the desired variable x′soll is filtered using a low-pass filter 24 and the first desired variable xc,soll for the first drive shaft 20a is generated in this manner. The first desired variable xc,soll is subtracted from the desired variable x′soll using a subtractor 26 and the second desired variable xf,soll for the second drive shaft 20b is generated in this manner.
FIG. 6 illustrates another implementation of the dividing unit, which is known from the prior art, in the form of the dividing unit 23′. In FIG. 6, the same elements are provided with the same reference symbols as in FIG. 5. The embodiment according to FIG. 6 differs from the embodiment according to FIG. 5 only in that, in order to compensate for the temporal delay in the desired variable xc,soll, as caused by the low-pass filter 24, the desired variable x′soll is delayed by a particular time using a delay unit 25 before it is supplied to the subtractor 26 as an input variable.
FIG. 7 again illustrates the drive system shown in FIG. 6 in a simplified manner. In this case, the same elements are provided with the same reference symbols as in FIG. 6. In this case, the first drive shaft 20a has a transfer function G(s) and the second drive shaft 20b has a transfer function F(s). The overall position xist of the machine element 8, that is to say its position with respect to the machine bed 35, results from adding the first actual variable xc,ist and the second actual variable xf,ist.
With conventional methods, the overall dynamics of the machine are determined by the regulating dynamics of the sluggish first drive shaft (coarse drive shaft). The potential of the dynamic second drive shaft (fine drive shaft) is thus not fully exploited.
Relatively large contour errors also generally occur in the known movement dividing methods. Overshooting when the desired variable changes rapidly and contour expansion in the case of circular contours to be traced by the machine element often occur in the known methods, for example.
An egg-shaped contour thus results from a circular contour to be traced by the machine element, for example.
It would therefore be desirable and advantageous to provide an improved to obviate prior art shortcomings and to move a machine element of an automation machine having redundant kinematics, during which contour errors of a contour to be traced by the machine element are reduced.
The contour error is here the difference between a predefined desired contour and the actual contour actually traced by the machine element.
The invention also makes it possible to increase the dynamics of the movement of the machine element.